The present invention relates to piezoelectric sensors, and particularly relates to piezocomposite acoustic sensors having a so-called 1-3 or 2-2 connectivity.
Typical 1-3 and 2-2 type piezocomposite acoustic devices are described in above-reference U.S. Pat. No. 5,340,510. In the 1-3 device, a one-dimensionally connected ceramic phase, i.e., an array of parallel rods, fibers, or other one-dimensionally extending fine ceramic elements is contained within a three-dimensionally connected polymer matrix. In the 2-2 device, a two-dimensionally connected ceramic phase, i.e., an array of parallel blades or plates is laminated with layers of a two-dimensionally connected polymer matrix. In either type of device, the ends of the elements are exposed at opposing planar surfaces of the ceramic/polymer composite. Typically, the electrodes are applied to these opposing planar surfaces. The ceramic phase is poled along the length (d.sub.33) direction of the ceramic elements, i.e., between the opposing, electroded, planar surfaces. To optimize the sensitivity of the devices, it is necessary to decouple the piezoelectric d.sub.33 and d.sub.31 coefficients, i.e., to minimize the effect of the acoustic vibration on the sides of the rods or blades.
In the field of piezocomposite sensors, it is well known that the sensitivity of the sensor is often highly dependent on the ambient pressure surrounding the sensor. This is particularly apparent at high pressures of up to 10,000 psi (about 70 MPa) or higher, e.g., in deep underwater hydrophone applications. Such high pressure applications have created a trade-off between sensitivity, on the one hand, and stability and robustness, on the other, of prior art devices. Increasing the pressure on the devices has resulted in a loss of sensitivity and, frequently, damage to the devices. Increasing the stability of the device, to decrease damage due to ambient pressure, has also decreased the sensitivity of the prior art devices. Additionally, minimization or optimization of the size and weight of the devices for certain applications must be balanced against the need for robustness in the devices.
Accordingly, it is an object of the present invention to provide a piezoelectric acoustic sensor which overcomes the disadvantages of the prior art.
It is another object of the invention to provide a piezoelectric acoustic sensor with high sensitivity and high robustness.